voith.com Extending uptimes for tugs with the Voith Schneider Propeller (VSP) Case study SHIPBUILDING & EQUIPMENT PROPULSION & MANOEUVRING TECHNOLOGY Extending uptime for tugs SEAKEEPING BEHAVIOUR Rolling movements are often the limiting factor for tug operations in waves. However, the Voith Schneider Propeller (VSP) with its fast and dynamic thrust adjustment, enables efficient active roll stabilisation and dynamic positioning (DP). This opens up new opportunities to increase the efficiency of tug operations, write Dr Dirk Jürgens and Michael Palm from Germany’s Voith GmbH. Tug rolling motions are often the limiting factor in offshore applications. While the waves counter LNG carriers from an optimal direction – from bow or stern – tugs often have to operate un- der the worst beam wave conditions. At a moderate significant wave height of Hs = 1.9m, roll angles of up to 26.7° were measured [5], with significant implica- tions for crew welfare and productivity. The VWT or RAVE Tug is a well- heberrechtlich untersagt. proven design and the Carrousel Rave Tug (CRT) [6] offers scope to deploy active Voith Roll Stabilization (VRS). As a re- sult, roll movements can be reduced con- siderably, by as much as 70% on tugs. The basis for the VRS is the fast response of the VSP [7], [8]. This article explains the effect of VRS using calculations, model tests and cus- tomer feedback as examples. The conclu- sion is that through the targeted use of Figure 1: Voith Water Tractor, Forte, equipped with two Voith Schneider Propellers (VSP36EC) VRS to reduce roll, the operating times and the electronic Voith Roll Stabilization (VRS) Source for all images and figures: Voith of offshore tugs can be significantly ex- ugs must now work in bigger waves because today’s larger vessels require Tthem to make line connections ear- lier, particularly in areas where consider- able waves build up [1]. But the effect of waves can be detrimental to the seakeep- ing characteristics of tugs, including limi- tations due to rolling motions, fluctuating line forces and the reduction of propeller forces due to ventilation and inflow speed to the propeller because of waves, current and vessel motions. The SAFETUG [2], [3] project re- vealed that these reductions of line forces were significant for the azimuth stern drive (ASD) tug analysed in the project, whereas the Voith Water Tractor (VWT) had only small reductions due to its differ- ent seakeeping behaviour. There are two reasons for this: firstly, the Voith Schnei- der Propeller (VSP) is located deep inside the ship and secondly, VSPs are not affect- ed by ventilation [4] because of the way in Figure 2: Voith Schneider Propeller Figure 3: Blade size of a modern VSP which thrust is generated. (X-ray view) (4-MW VSP unit) 10 Ship& Offshore | 2021 | Nº 1 © DVV Media Group GmbH Persönliche Ausgabe, , DVV Media Group GmbH Belegexemplar, Hamburg, Kd.Nr.: 910101010, Abo-Nr. 521925. Weitergabe an Dritte ur SHIPBUILDING & EQUIPMENT PROPULSION & MANOEUVRING TECHNOLOGY Bridge personnel can preselect the power range to be applied to roll stabilisa- Extending uptime for tugs tion, which operates through the propeller both at zero speed – in DP mode, for exam- SEAKEEPING BEHAVIOUR Rolling movements are often the limiting factor for tug operations in waves. ple – or when the tug is under way. However, the Voith Schneider Propeller (VSP) with its fast and dynamic thrust adjustment, enables efficient Roll stabilising tanks are no longer re- active roll stabilisation and dynamic positioning (DP). This opens up new opportunities to increase the quired and thus there is no reduction of efficiency of tug operations, write Dr Dirk Jürgens and Michael Palm from Germany’s Voith GmbH. payload and the VRS can be integrated with other anti-roll systems if necessary. Increased uptime is supplemented by im- Tug rolling motions are often the proved crew comfort and vessel safety. limiting factor in offshore applications. While the waves counter LNG carriers Simulation of roll damping from an optimal direction – from bow In order to quantify the effectiveness of the or stern – tugs often have to operate un- VRS, numerical roll damping simulations der the worst beam wave conditions. At on a typical VWT have been conducted. a moderate significant wave height of Hs Figure 8 shows the lines plan of the vessel. = 1.9m, roll angles of up to 26.7° were The main particulars are listed in Table 1. measured [5], with significant implica- Figure 4: Thrust generation of a VSP: two thrust examples The tug is equipped with two VSPs with a tions for crew welfare and productivity. blade orbit diameter of 3.2m, a blade length The VWT or RAVE Tug is a well- of 2.65m and a nominal input power of heberrechtlich untersagt. heberrechtlich untersagt. proven design and the Carrousel Rave Tug 2.7 MW each. (CRT) [6] offers scope to deploy active Voith Roll Stabilization (VRS). As a re- sult, roll movements can be reduced con- LWL [m] 37.50 siderably, by as much as 70% on tugs. The BWL [m] 13.82 basis for the VRS is the fast response of the T [m] 3.75 VSP [7], [8]. D [m³] 1,242 This article explains the effect of VRS GM [m] 3.41 using calculations, model tests and cus- rxx/B 0.297 tomer feedback as examples. The conclu- Table 1: Main particulars sion is that through the targeted use of Figure 1: Voith Water Tractor, Forte, equipped with two Voith Schneider Propellers (VSP36EC) VRS to reduce roll, the operating times and the electronic Voith Roll Stabilization (VRS) Source for all images and figures: Voith of offshore tugs can be significantly ex- The project used simulation software, IMPRES, developed at the Institute of Flu- id Dynamics and Ship Theory of the Tech- ugs must now work in bigger waves Figure 5: Thrust control principles of VSP and Z-drive thrusters nical University Hamburg and based on the because today’s larger vessels require Cummins equation [9]: Tthem to make line connections ear- lier, particularly in areas where consider- tended. Two tugs have been equipped position of the blade oscillations have to able waves build up [1]. But the effect of with VRS so far: the offshore tug Forte, be changed, thrust can be adjusted quickly. waves can be detrimental to the seakeep- owned by Edison Chouest Offshore Inc In dynamic positioning (DP) mode, the ing characteristics of tugs, including limi- (Figure 1), and the Japanese tug Shinano X-Y logic has particular benefits because This equation describes the motion of tations due to rolling motions, fluctuating Maru. the force requirements of the DP system a ship over time due to arbitrary external → line forces and the reduction of propeller can be met quickly, separated into longitu- forces F(t). M and A are matrices stating forces due to ventilation and inflow speed Functional principle of the VSP dinal and transverse thrust (Figure 5). the ships inertia and added mass, S, is a co- to the propeller because of waves, current The Voith Schneider Propeller is the efficient matrix for linear restoring forces and vessel motions. ship’s propulsion system. It provides fast Voith Roll Stabilization (VRS) and moments. The convolution integral The SAFETUG [2], [3] project re- and accurate thrust, steering and stabi- The VSP can generate thrust in longitudi- models hydrodynamic damping forces and vealed that these reductions of line forces lisation forces simultaneously in both nal and transverse directions and can be fluid memory effects due to radiated waves. were significant for the azimuth stern longitudinal and transverse directions. adjusted quickly in terms of magnitude and Ogilvie [10] showed that this hydrodynam- drive (ASD) tug analysed in the project, Figure 2 shows the inner structure of the direction, enabling the VSP to generate ic radiation force can be determined using whereas the Voith Water Tractor (VWT) VSP. Figure 3 shows the currently larg- roll-stabilising moments, thereby reducing added mass and damping coefficients from had only small reductions due to its differ- est blade of a VSP for a 4-MW unit. The roll. When the vessel encounters an incom- efficient frequency domain calculations. ent seakeeping behaviour. There are two thrust is generated according to an X-Y ing wave, sensors measure the roll accelera- For better numerical handling, IMPRES reasons for this: firstly, the Voith Schnei- logic. Unlike an azimuth thruster, longi- tion and the system immediately calculates uses a modified version of the Cummins der Propeller (VSP) is located deep inside tudinal and transverse thrust can be gen- and then applies the restoring force to equation [11]: the ship and secondly, VSPs are not affect- erated independently of each other. counteract the rolling motion of the vessel. ed by ventilation [4] because of the way in Figure 2: Voith Schneider Propeller Figure 3: Blade size of a modern VSP Figure 4 shows two thrust examples. The working principle of VRS is explained (X-ray view) (4-MW VSP unit) which thrust is generated. Since only the amplitude and the phase in Figure 6 and Figure 7. > 10 Ship& Offshore | 2021 | Nº 1 Ship& Offshore | 2021 | Nº 1 11 © DVV Media Group GmbH Persönliche Ausgabe, , DVV Media Group GmbH Belegexemplar, Hamburg, Kd.Nr.: 910101010, Abo-Nr. 521925. Weitergabe an Dritte ur © DVV Media Group GmbH Persönliche Ausgabe, , DVV Media Group GmbH Belegexemplar, Hamburg, Kd.Nr.: 910101010, Abo-Nr. 521925. Weitergabe an Dritte ur SHIPBUILDING & EQUIPMENT PROPULSION & MANOEUVRING TECHNOLOGY element methods based on potential theory are used in IMPRES. In linear frequency domain methods, the forces acting on the ship’s hull are sepa- rated into hydrodynamic mass and damp- ing forces because of the movement of the hull in still water (radiation) and the hydro- dynamic forces acting on a fixed ship hull in waves (excitation).